More and more digital circuits are being employed in automotive electronics such as automotive audio electronics. Consequently, there is a need for a relatively constant 5 volt voltage supply.
For audio products, the more efficient switching power supplies create undesirable side effects such as increased electromagnetic interference (EMI). EMI impairs radio reception. Consequently, linear-type voltage regulators have advantages over switching-type voltage regulators. Linear regulators have less EMI radiations, but they are also less efficient as described in Application Note 32 of Linear Technology Company.
Linear voltage regulators require the use of a large heat sink to dissipate wasted power from the voltage regulator. The wasted power primarily comes from the difference between input and output potentials resulting from instantaneous current requirements of the load. Such a large heat sink increases the volume and weight of the product. Therefore, it is desirable to have a voltage regulator circuit that is more efficient but that produces less EMI than prior art voltage regulator circuits.
German patent document 3 105 369 discloses a DC voltage regulator having two integrated circuit regulators connected in series between a load and a DC supply.
U.S. Pat. Nos. 3,600,667, 4,535,282, 4,074,182 and 4,611,162 all generally disclose voltage regulator circuits having two regulators. In addition, Japanese patent document 57-34217 discloses a similar-type circuit.